js数组去重的四种方式

// 删除重复的
function only(arr){
	for(var i=0;i<arr.length;i++){
		for(var j = i+1;j<arr.length;j++){
			if(arr[i]===arr[j]){
			    arr.splice(j,1);
			    j--;
			}
		}
	}
	return arr;
}
console.log(only([6]));//[6]
console.log(only([1,9,8,8,0,6,0,6]));//[1, 9, 8, 0, 6]

// 往新数组中插入不重复的元素或在最后一个位置的重复元素
function only(arr){
var newArr = [],
len = arr.length;
for(var i = 0;i<len;i++){
    for(var j = i+1;j<len;j++){
        if(arr[i]===arr[j]){
			j = false;
			break;
    	}
	}
	if(j){
    	newArr.push(arr[i]);
	}
}
return newArr;
}
console.log(only([6]));//[6]
console.log(only([1,9,8,8,0,6,0,6]));//[1, 9, 8, 0, 6]

//往新数组中插入不重复的元素或在最后一个位置的重复元素
//难理解一些，关键是“j = ++i;”，相当于开启新一轮的i循环（外层循环）
function only(arr){
    var newArr = [],
    len = arr.length;
    for(var i = 0;i<len;i++){
        for(var j = i+1;j<len;j++){
            if(arr[i] === arr[j]){
		j = ++i;
	    }
    	}
	newArr.push(arr[i]);
    }
    return newArr;
}
console.log(only([6]));//[6]
console.log(only([1,9,8,8,0,6,0,6]));//[1, 9, 8, 0, 6]

//将数组元素设为对象属性，值为true；如重复，不再添进数组
function only(arr){
    var newArr = [],
        obj = {},
        m;
    for(var i = 0;(m = arr[i]) !== undefined;i++){
        if(!obj[m]){
            newArr.push(arr[i]);
            obj[m] = true;
        }
    }
    return newArr;
}
console.log(only([6]));//[6]
console.log(only([1,9,8,8,0,6,0,6]));//[1, 9, 8, 0, 6]